By Nancy O'Donnell
Albany Times Union
Thatch is an intermingled layer of partially decomposed and decayed grass stems, plant crowns, various types of roots (including rhizomes and stolons, depending on the variety of turf grass grown) as well as other organic debris that accumulates at the soil surface.
Although it's often the dreaded six-letter-word of the turf world, thatch is really not so bad. Healthy lawns need a layer of thatch but no more than one-half inch at any given time.
Tiny microbes break down the thatch layer into usable nutrients the same way leaves and other organic amendments are broken down when you till them into your garden. It Is Mother Nature's personal recycling program for lawns, but the ticket to success is that the thatch is never allowed to accumulate over a half-inch.
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A proper thickness of thatch does for lawns what mulch does for your landscape plants; it insulates the soil so that temperature fluctuations are moderate. It also helps conserve soil moisture, deter weeds and, as mentioned, when decomposed adds important nutrients to the soil.
When conditions are favorable (moisture, air circulation, temperature, soil compaction, pH), the microbe production rate skyrockets. But when just one of these conditions is out of kilter, they begin to go on strike.
Problems arise when the thickness exceeds a half-inch. Excess accumulation becomes compacted by snow, rain and foot traffic, which in turn decreases air circulation and moisture penetration, two elements vital for microbe activity.
In addition, if too much thatch prevents rain from reaching the roots of the grass plant, the roots turn upward in search of water, leading to drought intolerance. As the roots turn upward they tend to heave the plant's crown up out of the soil, giving the lawn a "puffy" look. These elevated crowns in turn are scalped by the mower blade, leaving them weakened, if not destroyed.
With heavy rainstorms, thatch-laden lawns often show poor seepage; water pools first and then slowly drains down. And with increased compaction and decreased air circulation, this soaking-wet thatch layer takes longer to dry, creating a nice environment for insects and diseases.
Now, if rain can't penetrate, don't plan on fertilizer or pesticide applications getting through. Thick thatch will keep fertilizers and pesticides from reaching the root zone for absorption. So managing your lawn's thatch is important for its health and your wallet.
To check the thickness of your thatch layer, separate an area of lawn with your fingers. You'll notice a brown layer between the base of the grass plant and the surface of the soil. This is the thatch. The best way to measure is to remove a tiny patch/core that includes soil, roots, thatch and the grass plant then, with a ruler, measure the thickness of the brown layer.
Proper lawn care (fertilization, fall clean-up, soil pH, irrigation) goes a long way in controlling thatch buildup, and, contrary to popular belief, grass clippings don't significantly contribute to thatch. Studies have found that grass has a rapid decomposition rate due to its biological makeup, making it a feast for microbes. So the removal of clippings every time you mow isn't necessary.
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However, if you miss a few dates with your mower and large clumps result, it's best to remove them to prevent smothering the underlying plants.
When thatch becomes a problem, David Chinery, turfgrass specialist for Cornell Cooperative Extension, suggests the following:
Use a power dethatcher, aka a power rake, on heavy thatch (1-inch-deep or more).
This tool, available at rental companies, rakes up the thatch and lays it on top of the lawn. The thatch can then be easily removed and recycled by adding to your garden and tilling in. The tine depth on a power rake is adjustable; don't set it too deeply to avoid damaging grass plants. Power rakes are best used in early autumn, when the lawn is dry, and prior to any fertilizer treatment.
A core aerator is another piece of power equipment you can easily rent. With an aerator, small cylinders (3 to 4 inches deep) are extracted from the soil and left on the turf surface.
